A pervasive problem in threaded fasteners is to prevent a threaded collar that has been tightened onto a threaded pin from coming loose in use. Locknuts, lock washers, adhesives, and out-of-round collar sections are well-known means for resisting the tendency of a collar to work loose.
While each of the known lock means meets the locking requirement at least to some extent, they generally present limitations and introduce problems of their own.
It is an object of this invention to add to the collar-locking resources a fastener structure, tool, and method which does not require additional structural pieces such as lock washers, critical dimensions in the production article to produce a locking action, or foreign substances such as adhesives. A simple localized distortion of a structurally unimportant portion of the pin or collar, after tightening down the collar, is all that is needed.
This invention employs an externally threaded pin and an internally threaded collar. Their threads are so shaped and proportioned that the collar can be run freely onto the pin and tightened down without impediment. Known thread lock arrangements often include lock means which react while the collar is being run down. As a consequence, the torque actually applied between the threads, and the resulting axial preload in the resulting joint, are rendered uncertain. An example of such prior arrangements is prevailing lock arrangements where the collar is initially pressed out of round, and the forces generated by its restoration to round out the collar are the prevailing forces. Another example is where a lip on the collar is swaged into a groove on the pin by an adjacent face of a washer while the collar is being tightened down. These are useful and effective devices, but they do suffer from the coincidence of the torquing and locking functions.
It is an object of this invention to provide a threaded system that can be freely tightened, and then, after the desired torque is attained, the system can be locked without disturbing the applied torque level, or the axial pre-load.